1. Field of the Invention
The present invention relates to a head mounted display apparatus, and more particularly, to an adjustable head mounted display apparatus for video images or computer games, wherein the head mounted display apparatus is manually adjustable depending on an eye bridge span of a user while maintaining a constant optical distance between the eyes of a user and a target picture in the apparatus. As a result, a stable picture is supplied to the user, which prevents the user's eye fatigue from increasing.
2. Description of the Background Art
In general, a head mounted display apparatus is employed for playing virtual reality games or experiencing virtual realities. FIG. 1 is a typical structure of a head mounted display apparatus. As shown therein, an outer casing 10 includes a pair of display units 20 disposed at respective front sides thereof in order for a user to view therethrough pictures generated in the apparatus. A grip 30 is attached to each side of the outer casing 10 to facilitate its mounting on a user's head.
An internal structure of the conventional head mounted display apparatus will now be described. An optical system is respectively disposed in each side portion of the case so that a user can view pictures generated therein. The optical system will be explained with reference to FIG. 2. A liquid crystal display (LCD) 40 is disposed in the optical system to generate pictures. A backlight 50 is disposed to the rear of the liquid crystal display 40 along an optical path 70 so as to improve the brightness of the liquid crystal display 40. Also, a reflection plate 60 is disposed to the rear of the backlight 50 along the optical path 70 in order for the light from the backlight to beam towards the liquid crystal display 40.
A reflection mirror 80 is slantingly disposed in front of the liquid crystal display 40 along the optical path 70 so as to reflect by 90 degrees the pictures received from the liquid crystal display 40. A lens 90 is disposed between the reflection mirror 80 and a display unit 20 along the optical path 70 of the light beam reflected from the reflection mirror 80 so that the pictures from the liquid crystal display 40 can reach a user's eye 95. At this time, because the liquid crystal display 40 is provided within a focal distance of a focal point 5 of the lens 90, the virtually imaged pictures viewed by the user become enlarged.
Referring to FIGS. 3A and 3B, the shaping of the virtual image according to an example of the conventional art will now be described in further detail. First, as shown in FIG. 3A, when an object is placed to the position which is outside of the focal point 5 with regard to the lens 90, the image of the object becomes shaped in a reversed real image to an opposite side of the lens 90. Also, as shown in FIG. 3B, when an object is placed between the focal point 5 and the lens 90, the image of the object becomes shaped in an upright virtual image to the same side as the object.
However, the above-described conventional head mounted display apparatus requires two liquid crystal displays because the optical system needs to be disposed in each display unit 20, thereby increasing production cost. Further, the two required backlights 50 disadvantageously increase electrical power consumption.
To solve the above problems, another example of the conventional art is disclosed, wherein a single liquid crystal display is adapted, and its mechanism will be described with reference to FIG. 4. The optical system of a head mounted display apparatus according to the other example of the conventional art includes a liquid crystal display 40 and a backlight 50 disposed behind the liquid crystal display 40. A reflection plate 60 is disposed behind the backlight 50 so as to reflect the light forwardly.
A half-mirror prism block 99 is disposed in front of the liquid crystal display 40 so as to reflect the images from the liquid crystal display 40 along the optical path 70 towards each side. A reflection mirror 80 is disposed to each side of the half-mirror prism block 99 along the optical path 70 so as to convert by 90 degrees the direction of the images reflected from the half-mirror prism block 99. Each lens 90 is correspondingly disposed between the reflection mirror 80 and a display unit which faces a user's eye 95 along the optical path 70. The lens 90 serves to enlarge the images to be focused on the user's eye.
However, the head mounted display apparatus according to the other example of the conventional art is not adjustable to the eye bridge spans of users. As a result, users whose eye bridge spans do not correspond to a preset span of the apparatus suffer increased eye fatigue, while also experiencing poor picture quality.